In this paper we have focused on the fusion between the physical and digital worlds. We have explained our design method based on scenarios: real task and activity scenarios as well as projected scenarios that describe the future activity of the user with the tools to be developed. Projected scenarios are therefore used as a support for predictive evaluation during the design. We applied our design method for the design and implementation of a mobile collaborative augmented reality (AR) system dedicated to a group of archaeologists prospecting fields: the hardware and software MAGIC platform. In the MAGIC platform, the technological solutions for the fusion of the two worlds include the gateway window as well as the "clickable reality" and "augmented stroll" techniques. Although our solutions are designed and developed for a given application domain, archaeological prospecting activities, our interaction techniques are generic. One of our research avenues is to prove this generic aspect of the designed techniques by developing a mobile collaborative game based on the MAGIC platform.